There is a developing requirement in the data communication field that multimedia applications be able to run over interconnected networks. More particularly, there is a developing requirement that the network be capable of meeting the needs of multimedia applications for guaranteed bandwidth and end-to-end maximum delays, i.e,. what is called a Quality of Service (QoS) requirement. Such QoS requirements imply that an interconnected network must be able to manage the available network bandwidth and response time even though these parameters are likely to change over time in ways that might normally impact the communication quality.
A known FDDI standard describes a dual counter-rotating fiber-optic ring operating at 100 MBps. A FDDI ring may be used in a network as a very high-speed backbone interconnecting Local Area Networks (LANs). The allocation of network-wide bandwidth over such an interconnected LAN domain is dealt with in European patent application 93480041.8 filed on Apr. 19, 1993, by the assignee of the present invention, the teachings of which are incorporated herein by reference. To manage the reservation of certain levels of QoS in such an interconnected LAN domain, two functional components are employed: an Allocator and a Requestor. The Allocator is the component responsible for maintaining an awareness of the capacity of the LAN components (i.e. bridges and segments) so that a determination can be made whether a particular request for a bandwidth allocation can be granted. The Requestor is the component responsible for making a request to reserve a certain QoS for an application.
On an FDDI segment, however, QoS requirements must be satisfied by usage of synchronous traffic. A Synchronous Bandwidth Allocator (SBA) is defined in European patent application 93480221.6 filed on Dec. 8, 1993 by the assignee of the present invention. The SBA is responsible for allocating synchronous bandwidth to applications requiring guaranteed bandwidth and predictable delay. A single SBA manages an FDDI segment, each FDDI segment has one and only one SBA actively managing all synchronous traffic. This reference teaches slave SBA agents which can monitor the FDDI segment and take on the role of a master SBA agent when needed to assure high availability of the SBA agent function.
To enable the two bandwidth allocation processes (the centralized allocation process from the QoS Allocator and the SBA agent process over FDDI segment) to coexist over the interconnected LAN domain, European patent application 93480041.8 discloses the use of a Third Party Requestor (3PR) agent. The 3PR agent receives from the QoS Allocator all information that it needs to ask for bandwidth reservation on the FDDI segment. The 3PR agent is able to act on behalf of the FDDI station that is the expected source of synchronous traffic and ask that bandwidth be allocated to the SBA. Depending on the SBA response, the 3PR agent will then respond to the QoS Allocator which will grant or deny the allocation over the whole path.